Conventionally, a valve device may include: a passage formation member defining a fuel passage for the flow of evaporative fuel evaporating in a fuel tank; a valve body housed in the passage to open and close the fuel passage; a biasing member biasing the valve body to close the passage; and a valve driver driving the valve body to an open position by providing enough force to the valve body to overcome the closing force of the biasing member.
The valve body of such a valve device may include a region of play or “play region” to more securely close the passage, where the closure state of the valve is maintained when the valve body is in the play region. That is, driving the valve body in the play region will not open the valve until the valve body is driven through the play region and past a closure release position.
When opening the passage, the valve body is driven through the play region at high speed, and the driving speed of the valve body is decreased after passing a closure release position and the valve is further driven at the lower speed to preset degree of opening, to more quickly open of the passage to a preset degree.
The driving speed is decreased after passing the closure release position to limit and/or prevent a steep inflow and outflow of the evaporative fuel accompanying the quick opening of the passage.
In order to quickly open the passage to the preset degree, both the play region and the closure release position should be accurately determined.
However, some parts of the valve body, such as rubber parts and parts of other elastic materials, may change shape over time and from use, such as from material abrasion, compression, and the like, which may cause a variation in the closure release position. Therefore, it may be necessary to adjust the closure release position over time.
The adjustment of the closure release position in the valve device based on determining an accurate position is disclosed in patent document 1 (i.e., Japanese Patent Laid-Open No. 2015-102009). In the configuration described in patent document 1, the accurate position determination is performed every time the vehicle is started, by driving the valve body toward the opening direction bit by bit, and by detecting an internal pressure of the fuel tank.
However, in order to determine the closure release position in patent document 1, the determination device observes the internal pressure of the fuel tank for a certain period of time after driving of the valve body in the opening direction, in order to consider the delay of the internal pressure change when the passage is opened. That is, the technique in the patent document 1 takes time to accurately determine the closure release position. Because the internal pressure change is so small when the passage is initially opened, i.e., when the passage is opened to a small degree, the detection of even a nominal internal pressure change is a time consuming process.